This invention relates to drive couplings, and is especially (but not exclusively) concerned with readily-disconnectable drive couplings for connecting a drive shaft in or on a fuel injection pump test machine to the driven shaft of a fuel injection pump under test on the machine.
It is already known in such test machines to use a drive coupling which provides for some measure of lateral flexibility while, at the same time, ensuring torsional stiffness. The reason why lateral flexibility is desirable is that the drive shaft on the test machine and the driven shaft of the fuel injection pump under test are frequently slightly misaligned laterally or are angularly out-of-line, usually because the person carrying out the test is not able to get the two shafts absolutely in alignment with each other when clamping or otherwise fixing the fuel injection pump on the test machine. By way of illustration, a typical drive coupling hitherto used in such test machines is shown in FIGS. 1 and 2 of the accompanying drawings, and this prior coupling will now be described. FIG. 1 shows the coupling in vertical section, while FIG. 2 is a section taken on the line II--II in FIG. 1.
For ease of description, the elements of the coupling will be stated in the order of drive input to drive output, i.e. from left to right in FIG. 1. It thus comprises a plate 10 having a shaft 12 for connection to the shaft of an electric drive motor or other prime mover in a fuel injection pump test machine. The plate 10 is connected by two bolts or screws 14 to a relatively thin flexible disc 16 arranged transversely of the rotational axis 18 of the shaft 12, the bolts 14 being angularly spaced by 180.degree.. Two further bolts 20 angularly spaced at 90.degree. to the two bolts 14 connect the disc 16 to an intermediate solid member 22. Another two bolts 24 at the same angular positions about the drive axis 18 as the two bolts 20 join the intermediate member 22 to a second relatively thin flexible disc 26. Two further bolts 28 at the same angular positions as the bolts 14 connect the disc 26 to a second solid member 30. Two clamping jaws 32 swivel on two pins 34 protruding from the solid member 30, the two pins 34 being formed as integral extensions of the bolts 28. The jaws 32 lie one on either side of the drive axis 18 and are brought towards each other by means of a transverse bolt 36 passing through each jaw. The jaws are adapted to clamp onto two drive dogs 38 forming part of an injection pump driven member 40 having a shaft 42.
As each of the two thin discs 16, 26 is relatively free to bend in planes at right angles to each pair of bolts 14, 20; 24, 28, the discs have conical flexibility whilst remaining relatively stiff torsionally. The end effect is that the coupling can accommodate either angular out-of-line shafts or laterally misaligned shafts whilst ensuring high torsional stiffness. In addition, the jaws 32 offer the facility of rapid connection of the coupling to the article to be driven (in this case the shaft of a fuel pump on a fuel injection pump test machine).